Page 1 Hans Peter Schwefel Wireless Networks II: Lecture 3, Spring04 Wireless Networks II: Performance & Cross-Layer Aspects by Hans Peter Schwefel • Mm1 Cellular Networks: GSM, GPRS, and UMTS • Mm2 Network Performance: Methodology • Mm3 Quality of Service • Mm4 Security aspects of wireless networks • Mm5 Reliability aspects, content & header compression www.kom.auc.dk/~hps/WN2_Sp04/
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Page 1 Hans Peter Schwefel Wireless Networks II: Lecture 3, Spring04 Wireless Networks II: Performance & Cross-Layer Aspects by Hans Peter Schwefel Mm1.
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Motivation: Quality of Service• Advantages of Packet-Based Transport (as opposed to circuit switched)
– Flexibility– Optimal Use of Link Capacities, Multiplex-Gain for bursty traffic
• Drawbacks– Buffering/Queueing at routers can be necessary– Delay / Jitter / Packet Loss can occur – Overhead from Headers (20 Byte IPv4, 20 Byte TCP)
• Advantages:– Fine Granularity: per flow treatment, flexible set of QoS parameters– Able to provide QoS guarantees (if admission, classification, scheduling is
performed correctly)• Disadvantages
– Scalability problem: management of state for each single flow– Complexity (already connection admission can be complex, e.g. effective
– Adspec: Network Resources on Path• Non QoS Hop-count• Available Path Bandwidth• Minimum Path Latency• Path MTU
– Sender Template: Filter Specification• IP source address, protocol type, port number, etc.
– Previous router on path
Page 12Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
IntServ: RSVP Messages II• Resv Message
– Next hop in path (receiver sender)
– Flow-spec• Tspec• Rspec
– List of Filter Specs (description of sender for which the reservation is intended)
– Reservation style• Wildcard filter: shared, one reservation for all senders• Fixed filter: distinct, one per sender• Shared explicit: one reservation for specified list of senders
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1 | 0 (a) | reserved | 7 (b) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2 | 5 (c) |0| reserved | 6 (d) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3 | 127 (e) | 0 (f) | 5 (g) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4 | Token Bucket Rate [r] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5 | Token Bucket Size [b] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 6 | Peak Data Rate [p] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7 | Minimum Policed Unit [m] (32-bit integer) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8 | Maximum Packet Size [M] (32-bit integer) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (a) - Message format version number (0) (b) - Overall length (7 words not including header) (c) - Service header, service number 5 (Controlled-Load) (d) - Length of controlled-load data, 6 words not including per-service header (e) - Parameter ID, parameter 127 (Token Bucket TSpec) (f) - Parameter 127 flags (none set) (g) - Parameter 127 length, 5 words not including per-service header
Reservation Types:
•Guaranteed Service: Bandwidth and Delay Guarantees, No Loss
•Controlled Load: Only Bandwidth Guarantee
Page 14Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
Additional Issues in QoS signalling• Inter-domain signaling• Off-path signaling• Arbitrary placement of initiator and receiver • Bi-directional signaling/ sender-initiated signaling• Mobility support• Implementation size & complexity (~own transport protocol on top of
IP, multicast support, etc.)• How to secure RSVP in a real-world environment
Page 15Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
QoS signalling scenarios
QoS
midcom
QoS QoS
Host A
Host B
State kept at more than two entities.
Protocol requires interaction with other protocols (routing, security, AAA, mobility, etc.)
AS 1249 AS15465 AS17
Bandwidth
broker
QoS Signalling
data
Bandwidth
broker
Bandwidth
broker
IN-Path
OFF-Path
Page 16Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
QoS Solutions III: DiffServ• Basic Idea: reduce queueing delay/loss for critical traffic by preferential
treatment at routers (multiple queues) improve per-hop transmission behavior
• Packets marked by DiffServ Code Points (DSCPs, 6bit)
• Various scheduling disciplines at routers possible (e.g. static priority, weighted fair queueing)
• Advantage: Simple and scalable
• Problem: No performance guarantees unless used in conjunction with connection admission and traffic shaping/policing at ingress routers
SLA
CustomerNetwork
CustomerNetwork
SLA
SLA DiffServDomain
Border Router
Host
EdgeRouter SLA: Service Level Agreement
Page 17Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
Per Hop Behaviour
Differentiated Services (DS) Byte
CurrentlyUnused
Version IHL Total LengthIdentification Flags Fragment Offset
Time to Live Protocol Header ChecksumSource Address
Destination Address
Destination Address
Source Address
Version Flow LabelPayload Length Next Header Hop Limit
IPv4 IPv6
Traffic ClassTOS
17
DiffServ Code Points (DSCP)
Page 18Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
DiffServ: Influencing QoS• At Border Routers
– Traffic classification and Marking DiffServ Class (e.g. EF, AF, BE)
• Two thresholds: Commited Information Rate,Peak Information Rate
• Time-sliding window for measurement of average rate
• At Interior DiffServ Router– Scheduling: Strict Priority, Weighted Fair Queueing, etc.
– Buffer Management, e.g. Random Early Drop RED, RIO• Possibly different drop precedence
Page 19Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
47.1
47.247.3
12
1
2
1
23
3
IP 47.1.1.1
IP 47.1.1.1
QoS Solutions IV: Traffic Engineering
• TE = distribute traffic over network links in order to avoid congestion• IP routing (OSPF, IS-IS, RIP, etc.)
– Based on destination IP address– No possibility for distinguishing traffic classes– Modification of link costs possible, but implications on link utilizations not straightforward
• Alternatives– QoS Routing: Use QoS parameters for path selection
– Establishment of explicite paths• Automatically• Via network management• Approaches:
• Tunneling: e.g.L2TP, PPP
• Multi-Protocol Label Switching (MPLS)
Page 20Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
BR1
BR2
BR3
BR4
TR1 TR2
TR3TR4
AS1AS2 AS3
• Border Router (ingress) assigns label to packet• e.g. based on protocol type, DSCP, QoS demands, etc.
• Forwarding within MPLS domain based on assigned label• Necessary: establishment of Label Switched Paths (LSPs), using signalling protocols
• CR-LDP• RSVP-TE
• Egress router will remove label
Ingress routerreceives packetIngress router
receives packetPacket labeled
based onegress router
Packet labeled based on
egress router
Forwarding in the interiorbased on labels
Forwarding in the interiorbased on labels
Egress borderrouter pops
label and fwds.
Egress borderrouter pops
label and fwds.
MPLS: Principles
Page 21Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
Dynamic MPLS paths for aggregated traffic• Dynamic MPLS path setup using source routing
• Question:
– Trigger events?
– Requirements/QoS parameters for new path?
Page 22Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
QoS routing
• E.g. QoS routing based on RFC 2676 (Apostolopoulos, et al. - QoS Routing Mechanisms and OSPF Extensions; status: experimental)
• OSPF LSAs advertise
– Cost
– Residual bandwidth
– Delay of links
• Widest-shortest path algorithm:
– Among all paths with sufficient bandwidth
– choose among those with the lowest hop count
– If there are several feasible paths with identical hop count, choose the one with the highest residual bandwidth.
• Computation of routing tables at each node using a modified Bellman-Ford algorithm
3 scheduling of RLC/MAC blocks within a TBF (BSS, RLC/MAC)
QoS management in GPRS follows a three-stage principle:
QoS negotiation at Packet Data Protocol (PDP) context activation
radio resource assignment at TBF setup
scheduling of radio blocks during ongoing TBF + QoS in IP transport (SGSNGGSN)
Page 25Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
GPRS Release 97: QoS profilesQoS in GPRS Release 97 is described by the parameters of the QoS profile
precedence class (4 classes)
reliability class (9 classes)
delay class (4 classes)
peak throughput class (9 classes)
mean throughput class (19 classes)
QoS profile is negotiated between MS and SGSN/GGSN at PDP context activation
QoS profile is not available in the BSS
no efficient MAC scheduling can be performed
Page 26Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
GPRS Release 99: Traffic classes
Conversational Audio Telephony 4-25 kbit/s < 150 ms
Data Telnet > 8 kbit/s < 250 ms
Streaming Audio Internet Radio (HQ) 32-128 kbit/s < 10 ms
Data FTP - < 10 ms
Interactive Data Web Browsing (HTML)
- < 4 s/Seite
Audio Voice Messages 4-13 kbit/s < 1 s
Background Data E-mail - -
besides the QoS profile four application-specific traffic classes are introduced (conversational, streaming, interactive, background)
Aggregate BSS QoS Profile (ABSQSP) is indicated to the BSS by the SGSN on demand
TypeTraffic class Application Data rate req. Delay req.
Page 27Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
PDP context activation(PDP = Packet Data Protocol)
1) MS initiates the PDP context activation2) connection admission control (CAC) in
the SGSN checks the requested QoS profile
3) GGSN installs downlink Traffic Flow Template
4) QoS profile is delivered to BSS5) BSS indicates radio priority to MS
PDP context setup and QoS
Activate PDP Context Req (QoS Req)
...
...
RLC/MAC CACCAC
InstallDL TFT
GPRS
Set radio
MS SGSN GGSNBSS
Create BSS PFC Req (ABQS)
Create PDP Context Res (QoS Neg)
(Radio priority)
Radio Resource Request
DeleteDL TFT
Activate PDP Context Acc (QoS Neg)
Create BSS PFC Acc (ABQS)
Create PDP Context Req (QoS Neg)
Deactivate PDP Context ReqDelete PDP Context Req
Delete PDP Context ResDeactivate PDP Context Acc
Mapping to
PDP context
Delete PDPcontext
Admission control
Scheduling
setpriority
Page 28Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
Limit I
Shared(priority to premium)
Premium andinteractivetraffic increase
Implementation example: CACLowtrafficload
Backgroundtraffic increases
Resources used by
traffic streams
Premium
Shared(priority to interactive)
Reserved tobackground
Interactive Background
Limit P
three traffic classes are regarded:
premium subscriber traffic
interactive traffic
background traffic
the aim of an optimized CAC policy is the compromise between:
efficient use of resources
guarantee of negotiated QoS
this can be achieved by suitable choice of the limits P and I
Page 29Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
Implementation example: MAC scheduler
Best effort
Standard
Premium„Gold Card“ service
Background
Interactive
Conversational
Streaming
FIFO, RR, EDD, etc.
ApplicationQoS profile
SubscriberQoS profile
Priority
differentiation by subscriber QoS classes differentiation by application QoS classes scheduling of the different traffic class queues (priority-based) scheduling of TBFs within the traffic class queues (round robin)
Page 30Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
UMTS QoS: Bearer Hierarchy
TE MT UTRAN/GERAN
CN IuEDGENODE
CNGateway
TE/AS
End-to-End Service(IP Bearer Service)
TE/MT LocalBearer Service
UMTS BearerService
External BearerService
UMTS Bearer Service
Radio Access BearerService
CN BearerService
BackboneBearer Service
Iu BearerService
Radio BearerService
PhysicalRadio
Service
PhysicalBearer Service
Air Interface
3G GGSN3G SGSNRAN
User Equipment
Mapping of Parameters between bearer levels is implementation dependent!
Token bucket: bucket size = k*MaxSDUsize; token rate=guaranteed bitratek=1 in Rel. 99; Note: for speech traffic, maximum bitrate = guaranteed bitrate (TS 25.413)
• Source statistics descriptor (`speech´, `unknown´)Could be used to compute effective bandwidths (multiplex gain)
• Transfer delay (ms)limit 95percentile of delay distribution of all delivered SDUs
• SDU error ratiofraction of lost or detected erroneous SDUs
• Maximum SDU size (bytes)
Page 33Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
UMTS Bearer: Range of Traffic/QoS Parameters(Source TS23.107, V5.2.0)
AMR: SDU size 100-200 bit (20 ms inter-SDU time)
Subflows on Radio Access Bearer (25.413, 26.xxx)
Page 34Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
Mapping GPRS/UMTS classes to DiffServ classes
UMTS QoS class DiffServ class ReasonConversational class Expedited forwarding class low latency and jitter
Streaming class Assured forwarding Class 4
low variation of delay
Interactive class Assured forwardingClass 3
low latency(but not as low as in conversational class)
Background class Assured forwardingClass 2 or class 1 or best effort (class 0)
no special requirement for this class except reliability
Page 35Hans Peter Schwefel
Wireless Networks II: Lecture 3, Spring04
UMTS QoS Signalling: 3GPP ArchitectureNew Entities in UMTS Rel‘5:• Policy Control Function (co-located to P-CSCF)• IP Bearer Service Manager (Policy Enforcement